Influence of prostate volume on dosimetry results in real-time 125I seed implantation.

Purpose: Achieving a minimal dose of 140 Gy to 90% of the prostate (D90) on postimplant dosimetry has been shown to yield improved biochemical control by 125I brachytherapy, and a D90 >180 Gy can be associated with increased long-term toxicity of seed implantation. Significant enlargement of the prostate on postimplant CT compared with the ultrasound (US) volume at implantation (CT/US ratio) has been associated with lower dose results, but other factors predicting for high or low doses are not well established. We determined whether the prostate size at implantation influenced the CT/US ratio results affecting postimplant dosimetry or predicted for D90 values <140 or >180 Gy in patients implanted with 125I in a community hospital setting.